The present invention relates to precision approach path indicator systems (PAPIs) used in airports to provide approach slope guidance for aircraft approaching an airport runway, and light assemblies useful in such systems. More particularly, the present invention relates to PAPIs and light assemblies for use therein which provide substantial and important advantages and/or benefits relative to the prior art systems and assemblies.
Precision approach path indicator systems (PAPIs) are known airport lighting aids. As commonly employed, PAPIs use a single row of either two or four light units including halogen or similar lamps. The row of either two or four identical light units is placed on one side of the runway in a line perpendicular to the runway centerline to define the visual glide path angle. The light units each have a white segment in an upper part of the beam and red segment in a lower part of the beam separated by a pink transition zone. In the two-light system, for example, a Type L-881 system, the lights are positioned and aimed to produce a signal presentation wherein a pilot on or close to the established approach path sees the light unit nearest the runway as red and the other light unit as white. When above the approach path the pilot sees both light units as white; and when below the approach path the pilot sees both light units as red.
In the four-light system, for example, Type L-880, PAPI system, the signal presentation is such that a pilot on or close to the established approach path sees the two light units nearest the runway as red and the two light units farthest from the runway as white. When above the approach path the pilot sees the light unit nearest the runway as red and the three light units farthest from the runway as white; and when further above the approach path the pilot sees all the light units as white. When below the approach path the pilot sees the three light units nearest the runway as red and the light unit farthest from the runway as white; and when further below the approach path the pilot sees all light units as red.
The visual glide path angle provided by the PAPI is the center of the on-course zone, and is normally 3 degrees (of an arc) when measured from the horizontal, but may vary, for example, if jet aircraft are supported by the airport, if obstacles to flight are located at the airport, or if elevated terrain affects the approach to the airport. Other considerations in siting the PAPIs indicator lights include whether the terrain drops off rapidly near the approach threshold, and whether severe turbulence is experienced on approach. On short runways, the PAPI system indicator lights are located as near the threshold as possible to provide the maximum amount of runway for braking after landing. Thus, the PAPI system indicator lights are often positioned and aimed to produce a minimum Threshold Crossing Height (TCH), which is the height of the lowest on-course signal at a point directly above the intersection of the runway centerline and the threshold, and clearance over obstacles in the approach area.
PAPIs are very useful in providing approach slope guidance to aircraft approaching an airport. However, certain problems do exist. For example, the halogen or similar lamps used in the prior art PAPIs are relatively costly to operate and, in addition, have a relatively limited useful life. Although the lighting assemblies of such PAPIs are structured to facilitate relatively rapid lamp replacement, the cost of maintenance, particularly the cost and inconvenience of closing an airport runway in order to change lamps, represents a significant disadvantage to using such PAPIs. In addition, since providing accurate approach path guidance is very important in maintaining the safety of airport operation, lamps which become ineffective after relatively short periods of operation, even if they are relatively easy to replace, can create a significant detriment to airport safety.
There is a need for new PAPIs, for example new PAPIs which address one or more of the problems or disadvantages of the prior art PAPIs.